The main objective of the proposed research is to determine, by means of light microscopy, and scanning and transmission electron microscopy, the types of sensory structures used by schistosome cercariae and the distribution of these structures over the cercarial body. Such information, it is hoped, will provide a morphological basis for interpreting cercarial behavior which is important in finding, recognition, and penetration of suitable hosts, and possibly in finding specific sites within hosts. It was also hoped that knowledge of number and distribution patterns of "papillae" (argentophilic structures) may enable determination of the sex of schistosome cercariae and may be of systematic value in separating schistosome cercariae of different species, and possibly strains.